This invention relates to a trim angle sensor for a marine propulsion device and more particularly to an improved trim angle sensor that will provide a more accurate indication of the trim angle position through a wider range of movement than is possible with prior art type of devices.
In marine outboard drives (either an outboard motor or the outboard drive portion of an inboard/outboard drive), it is the common practice to suspend the outboard drive for pivotal movement about a horizontally extending tilt axis. This pivotal movement is employed for two purposes. First, it is employed so as to adjust the trim position of the outboard drive to the optimum angle for all running conditions; and second, it is employed so as to permit the outboard drive to be tilted up out of the water when not in use or for servicing.
In many instances, such mechanisms further include a trim angle sensor for providing a signal indicative of the adjusted trim angle of the outboard drive. This signal may be used either to provide an indication to a remotely positioned operator of the trim position or, alternatively, may be used in conjunction with such a remote indication and furthermore to function in a circuit for providing an automatically adjusted trim position. In such an application, the trim angle sensor provides a signal to the controlling circuit that indicates the actual trim angle of the outboard drive for processing through the circuit to change the trim angle, if necessary, to the optimum trim angle.
The type of trim angle sensors normally employed include, as a sensing element, some form of magnetically activated device such as a Hall effect sensor or a device in which a movable magnet actuates a sensor that has its resistance change in response to the change in magnetic force. Although such sensors are quite desirable, they are not accurate over a wide range of movement. By their very nature, magnetic sensors tend to have an output signal that varies similar to a sinusoidal wave. Thus, the accuracy of the sensor deteriorates under large degrees of movement resulting in either improper readings or the necessity for employing compensating circuits.
It is, therefore, a principal object of this invention to provide an improved trim angle sensor that is constructed in such a way that it will operate only over the linear phase of its motion.
It is a further object of this invention to provide a trim angle sensor employing a reduction system for insuring that large trim angle variations may be sensed in a linear manner by reducing the amount of movement of the sensor in relation to the actual amount of movement of the outboard drive.
It is a further object of this invention to provide an improved trim angle sensor embodying a gear reduction unit for this purpose.
When trim angle sensors are employed that utilize a reduction mechanism, such as a gear reduction, it is desirable to insure against backlash that could introduce incorrect readings into the system.
It is, therefore, a further objection of this invention to provide an improved trim angle sensor having a gear reduction unit and an arrangement for reducing backlash in the gear reduction unit.